A very tiny gamma ray detector

When you think of a radiation detector, you’re probably thinking of a Geiger tube and its high voltage circuitry. That isn’t the only way to measure gamma radiation, though, and [Alan] has a great circuit to measure even relatively weak radiation sources. It uses a very small photodiode, and draws so little power it’s perfect for projects with the smallest power budgets.

The detector circuit uses a miniature solar cell and a JFET wired up in a small brass tube to block most of the light and to offer some EM shielding. This, in turn, is attached to a small amplifier circuit with a LED, Piezo clicker, and in [Alan]’s case a small counter module. The photodiode is actually sensitive enough to detect the small amounts of gamma radiation produced from a smoke alarm americium source, and also registers [Alan]’s other more powerful radioactive sources.

The circuit only draws about 1mA, but [Alan] says he can probably get that down to a few micoAmps. A perfect radiation sensor for lightweight and low power applications, and gives us the inspiration to put a high altitude balloon project together.

There was actually a guy at UPenn(?) that was doing just that. It turns out that solar activity through some as yet explained mechanism (neutrinos have been proposed) actually influences radioactive decay and thus it doesn’t make a truly random reaction.

Not just that-but at domestic steel mills in the scrapyard (most “new” steel contains a lot of “old” steel). A single load of radioactive scrap can ruin your whole day.

As far as other forms of radiation detection-Argonne Natl. Labs invented a polymer a decade back that can detect neutron flux. I’m certain the TSA folks and the FBI have detectors based on that nowadays.

Since the the detonation of the first nukes most materials are contaminated anyway, not much (they are essentially entirely safe) but enough to make them useless for certain applications.

That gets really annoying if you have to do science where you need a radiation free hardware (like say detectors in particle-accelerators). Thats why WW1 ships that sank prior to the Manhatten project are so precious. The Metals in those are very clean and where sheltered against the fallout(s) on the bottom of the ocean.

Another good thing of those radiation detectors? You can always find you bananas ;)

One of the first things I had to do was have a total body count done before I could start working at Savannah River Site and the table I had to lay down on had to be made from pre WW2 metal due to all metal after has some radioactive material of some sort.
And yes the tech said that I did have a banana that am since there was a spike for potassium 40 a radioactive isotope that is in bananas.

One thing would be hard to do is to calibrate the detector, since Gamma sources are not an everyday item.

I even with a mica window I don’t know if this sensor will pick up alpha particles but might be a good beta. And if you have a old civil defense Geiger detector it has a beta source on the side of the case.

I wonder if it would get a bit more sensitive to (Gamma) radiation if you add some Diamond, Saphire or Glass in front of the Phototransistor to get the (Gamma-)radiation to slow down emitting Cherenkov radiation (light). Since the phototransitor is actually build for that it could work better.

Note that Gamma radiation IS light. It traveling into sapphire/etc. won’t generate Cherenkov radiation, but it might result in the Gamma being diffracted slightly. Diamonds do fluoresce under X-ray/Gamma… so there might some potential advantage.

@Poose I heard about Co-60 loaded belt buckles, just what you don’t need as a consumer..

I was horrified to see just how many were contaminated, over a lifetime ONE belt could add up to 400 chest X-rays worth, which is not a small amount of radiation at all.

Re. detectors, I made one using a mono CMOS video camera from B&Q and a sheet of silver paint coated mica, which later evolved into a sheet of thin pyrolytic graphite
as this is better for low energy particles such as alphas.
Something like 75% make it through a 0.1mm sanded sheet :-)
Decrease clock to increase sensitivity, the “sweet spot” is 4MHz instead of 13.5.
Something about increasing charge accumulation maybe?

Tried to publish it in electronics magazines but they said “too specialised”… :-(

Cool idea. I think a lot of people are unaware of how many devices are capable of detecting radiation even though that is not their primary function. In fact 99% of the people reading this have a decent radiation detection device in their possesion right now. Your camera phone. As I posted in a comment above, there is a serious Android app to use the phone’s camera as a radiation detector and they have even done calibration on several devices using the camera and comparing it’s sensitivity to high end detection equipment. See the app here: http://goo.gl/r005D
Here is a section of the app’s readme:
The App is using the camera sensor to detect radiation, like a geiger mueller counter, of course with a smaller area. We tested several mobile phones at the Helmholtz research facility in Munich, using a professional radiation device in the range of 2-10 µGy/h till 1-10 Gy/h (CS137 and CO60). The CMOS sensors can detect primary gamma radiation and some higher beta radiation (depends on the shieldings in the mobile phone). Typically not going into saturation as most GM tubes. See FAQ on our homepage for what you can measure and how.

Unfortunately no pictures that I am aware of, the problem is that it wasn’t as reliable as I’d hoped possibly due to the alphas “sand blasting” the row and column drivers for the sensor. If I made this again it would include a lead shield and just expose the centre of the chip…

If anyone wants to try this, please PM me on the forum or mandoline at cwgsy dit dah net yadayada.
remove at and morse to mail.

I did notice that really cheap and nasty ™ old webcams from laptops are quite good for this, even the plastic used passes a few alphas.
What would be really nice is if manufacturers used bare chips, but they probably don’t because they corrode in time like I found.

The problem would be fixed if the sensor was encased in say an Aixiz module with PG end window held in place with Epoxy and then silver painted and electroplated with a mask to protect the centre of the PG, and then backfilled with say argon and some silica gel..

If I were to update this, format it as a scientific quality report with data, and submit it to a major journal such as “Nature” or “Scientific American” do you think they’d publish it?

@Longfist yes I just noticed (facepalm!)

This also has implications for detecting of other “interesting” nuclides such as 40K and 137Cs at a substantial distance, the details of which are yet to be worked out.
Essentially this is a modification that might detect alpha particle entanglement which could carry a lot further than a simple alpha and also show information about the source not obtainable by any other method… !

There are quite of few project using PIN photodiodes already, mostly using the BPW-34, but also other types such as the BPW21, S1223, etc. There are a few that go even further, using large area, ultra sensitive photodiodes such as the PS100-7-CER (also expensive).
The main disadvantage is these constructions are quite insensitive when it comes to gamma radiation, and totally worthless for beta and alpha which are stopped in the plastic case of the tiny photodiodes.
Some builders went even further to dismantle the epoxy/glass casing to expose the semiconductor junction of the photodiode, and so making them able to detect alpha and beta as well.
The pulse is proportional to the energy of the incoming radiation allowing experimenters to create simple spectrography devices but the drawback is high energy radiation will not transfer the entire energy to the tiny photodiode layer, giving misleading results.

Also worth mentioning, in case people haven’t found this out some of the Apple desktops use an exposed chip on their cameras.
ie 19″ and 22″ Mac flat panels with the iSight camera, v2 and v3 use these.
I also located a similar sensor used in older Nokias and despite the color filters it still works fine.
A valuable method of “nuking” filters is a UV laser and this may ruin the camera for normal use but the alpha sensitivity remains.